One of the most dramatic weather phenomena on our planet is a stratospheric sudden warming: an abrupt change in the Arctic winter stratosphere in which temperatures can spike by as much as 90°F over a few days. Such warmings have been linked to profound shifts in weather at ground level, including frigid winter cold snaps in Europe and North America, and also to dramatic variations in the ionosphere, at several hundred kilometers above the ground. A new study reveals that ionospheric imprints of these warmings—which were previously studied only during daytime—may be even bigger at night, a finding that could improve space weather forecasting.

Sudden stratospheric warmings (SSWs) can be traced back to waves in Earth’s troposphere, the layer of atmosphere that begins at the ground and ends at about 10 kilometers above sea level. As air moves over big land features such as the Himalayas, giant Earth-spanning atmospheric waves form and move upward into the stratosphere, the atmospheric layer extending between 10 and 50 kilometers above Earth’s surface. These waves push cold air away from the North Pole, driving it to lower latitudes, and also affect atmospheric chemistry and ionospheric electric fields, potentially disrupting satellite navigation and telecommunications.

A long-standing debate is how much the different layers of the atmosphere are connected and to what extent something that happens in one region affects other areas far away. To explore that question, Goncharenko et al. looked closely at a major SSW that occurred in January 2013. They examined the density of electrons per square meter of atmosphere—a measure called total electron content—using a worldwide network of GPS satellites that monitor the ionosphere, a pulsating layer of charged ions from about 60 to 1,000 kilometers high above Earth. The team also used radio measurements to measure electron density over time and incoherent scatter radar, a technique that measures variations in the ionosphere at different heights.

They found a deep hole in the nighttime ionosphere so large that it covered nearly half the globe. In more southern latitudes, electron density was reduced fourfold to fivefold, while the decrease was closer to twofold near the equator. In the past, studies have suggested that SSWs generate shifts in the ionospheric electric field that ripple through the ionosphere. But the formation of the massive hole was more consistent with winds in a region of the ionosphere called the F region, the team reports. Such anomalies are not well studied and present a new avenue for research that could help scientists predict how SSWs affect space weather. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2018JA025541, 2018)

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